A. Field of the Invention
The present invention relates broadly to an internal drive mechanism in an air compressor and, more specifically, to a drive mechanism for use in a supercharger for an internal combustion engine or an air compressor of the type driven mechanically by the engine or other power source.
B. Discussion of the Prior Art
It is well known that in a supercharger or air compressor, increasing the volume of air charge delivered to the combustion chamber of an internal combustion engine will increase the output of the engine for a given displacement at a given engine speed. There are two basic types of superchargers, centrifugal and positive displacement. The centrifugal type is very efficient, providing the best ratio between unit dimensions and flow volume. The air compression in the centrifugal design is achieved using a scroll or scroll-shaped air chamber having a centrally located air inlet and an impeller rotatably disposed in the air inlet to draw in air and then the compress the air within the scroll. An air outlet connected to the combustion chamber delivers the compressed air to the engine. Centrifugal designs require high peripheral compressor-wheel or impeller velocities approaching or exceeding the speed of sound, which can be achieved with either an exhaust-driven direct-drive turbine compressor wheel combination, or a mechanical drive connected between the engine crankshaft and the input shaft of the supercharger. The overall speed ratio between the impeller and the crankshaft should be, practically, at least nine impeller rotations for every rotation of the crankshaft, and the outer external mechanical drive is usually limited to a step-up ratio of approximately three input shaft rotations for every rotation of the crankshaft. Thus a further internal step-up mechanism is desired to increase the impeller to three or four additional rotations for every rotation of the input shaft.
It is known in air compressors that a step-up ratio of 9 to 1 between power sources and the impeller is desirable. Presently this ratio has been attempted using external step-up drives only; however, such configurations result in relatively low speeds and low flow when compared to an air compressor with an internal step-up drive. Internal drives have in the past not been considered reliable for this intended use.
Previously known internal drive mechanisms have employed planetary traction drives, or gear drives. An example of an internal gear drive mechanism is disclosed in U.S. Pat. No. 5,224,459, issued to James Middlebrook. In general, traction drives or gear drives require lubrication, causing unwanted heat buildup, which thereby tends to reduce the density of the compressed air discharge. Planetary step-up ball and/or race drives require preloading of the mechanism to prevent slippage, due to the necessity of lubrication and traction to transmit rotational power. The preloading of these drives and the related lubrication causes further intrinsic heat buildup, thus further reducing the density of the compressed air discharge. Gear drives are undesirably noisy to operate, usually requiring hot engine oil to lubricate the gears and bearings, causing additional heat buildup, which also contributes to a reduction of the air density. In addition, the gear drives must be connected to the engine oil reserve, making them more difficult to install and maintain.